This invention relates to a dental handpiece and, more particularly, to a dental handpiece having a bearing protective member capable of preventing bearing oil shortage and terminating the suction of tooth debris into the inside of the bearing.
Up to now, a dental handpiece having a dental tool mounted thereon has been used extensively for tooth treatment. The conventional dental handpiece of the angle type is shown as an example in FIG. 5.
An angle type dental handpiece 50 has its foremost part constituted by a head housing 51 for loading a dental treatment tool 9 therein and a head housing jacket 52 connected to the head housing 51.
Within the head housing 51 at the foremost part of the dental handpiece is removably mounted a casing 57 made up of a cartridge casing 57a and a casing lid 57b. Within the casing 57 are arranged a bur sleeve 53 for receiving the dental treatment tool 9 via a reception opening 53a for securing the tool in position, a rotor 54 for rotationally driving the bur sleeve 53, an upper bearing 55 and a lower bearing 55' for rotatably supporting the bur sleeve 53 with respect to the head housing 51. A head cap 56 is threadedly mounted on the top of the head housing 51. Within the head cap 56 is mounted a chuck device, not shown, for removably holding the dental treatment tool 9 on thrusting or releasing a pushbutton 56a. Within the head housing jacket 52, there are an air supply passage 52a for supplying compressed air to the rotor 54 and an air discharge passage 52b for discharging the compressed air supplied into the inside of the head housing 51.
Radially outwardly of the bur sleeve 53 is mounted the rotor 54 in a spacing 58 between the upper bearing 55 and the lower bearing 55'. The rotor 54 acts as an air turbine rotated with the bur sleeve 53 by the compressed air supplied from the air supply passage 52a.
The above-described dental handpiece 50 has, however, a drawback that compressed air supplied via the air supply passage 52a for rotationally driving the rotor 54 is discharged to the outside of the head housing 51 via small gaps around the bearings 55, 55' exposed to the spacing 58, so that oil shortage tends to be produced in the regions of balls 55a, 55a' and retainers 55b, 55b'. Thus, it becomes necessary to replenish oil such as by oil spraying for lubricating or washing the bearings 55, 55' suffering from oil shortage. Although grease may be used in order to combat the problem of oil shortage, inconvenience may be produced such that the grease tends to flow out of the head housing 51.
There is also a problem that, during the standstill of the rotation of the air turbine, negative pressure tends to be produced within the inside of the head housing 51 and, under the pressure difference between the inside and the outside of the head housing 51, tooth debris, saliva or blood tend to be sucked from the outside into the inside of the head housing 51 via the pap between the bur sleeve 53 on the one hand and the head housing 51 and the casing 57 on the other hand, thus producing damages to the race surfaces or abrasion of the balls 55a, 55a' or the retainers 55b, 55b' of the bearings 55, 55'.